Hydraulic control system for die pads in presses



March 27, 1962 F. M. WILLIAMSON HYDRAULIC CONTROL SYSTEM FOR DIE PADS IN PRESSES Filed D60. 2, 1960 2 Sheets-Sheet 1 March 27, 1962 F. M. WILLIAMSON 3,027,151

HYDRAULIC CONTROL SYSTEM FOR DIE PADS IN PRESSES Filed Dec. 2, 1960 2 SheetsSheet 2 '0 /72 1 M0 I /fl2 A95 /d5 INVENTOR.

3 J72 aM/dY/Zawxsam M L 4 M nit rates This invention relates to mechanical presses of the ram type employing a movable die pad which is engaged by one or more hydraulically controlled pistons for moving the die pad to an extended position on the return stroke of the ram and which pistons resist movement of the die pad to its retracted position during the working stroke of the ram. The invention is more particularly directed to a hydraulic control system for controlling the flow of hydraulic fluid to and from the cylinders containing the pistons which engage the die pad.

in my Patent No. 2,842,357, issued July 8, 1958, I have disclosed a hydraulic control system for the die pads of a ram type press. The present invention is an improvement over the system disclosed in such patent and provides a greatly simplified and less expensive valve arrangement for controlling the flow of the hydraulic fluid to and from the working cylinders. in hydraulic circuits of this type it is important to circulate at least a part of the hydraulic fluid through the supply tank during each cycle of the press in order to prevent overheating of the fluid and the valve and passages. Heating of the liquid can also be minimized by reducing the velocity at which the hydraulic fluid flows through the lines and valve passages, and the present invention has as its object the provision of a hydraulic system of this type which is designed to obtain circulation of a part of the oil through the supply tank at each stroke of the press and to reduce the velocity of flow of the fluid so as to reduce the heat resulting from friction due to the fluid flow through the system. It is desirable to use hydraulic lines as small as possible because of their flexibility to move with the motion of the die. Large lines are cumbersome and present an obstruction.

A principal object of the invention is to provide a new and improved hydraulic control system for die pads in ram type presses.

Another object of this invention is to provide a system in which it is possible to use smaller lines from the tank by allowing the oil to flow through a plurality of lines to the tank during the small portion of the cycle when the velocity is very high.

Another object of the invention is to provide a control system of the type described which is comprised of a minimum number of parts to reduce the cost and increase the dependability thereof and which makes possible the use of relatively small diameter fluid conduits.

A further object of the invention is to provide a hydraulic control system of the type described which provides additional passage area for the flow of fluid to and from the supply tank during certain portions of the cycle of the press, thereby reducing the flow velocity of the fluid and eliminating excessive heating in the system.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. 1 is a schematic view illustrating a hydraulic Patented Mar. 27, 1962 control circuit for the die pad of a ram type press; and

FIG. 2 is a view similar to FIG. 1 illustrating a modified form of the invention.

In FIG. 1 there is illustrated a porL on of a crank type press ll) which includes a ram 12 driven by a crank in a conventional manner and carrying an upper die 14, and a lower die shoe 15 mounted on a bolster 18 and carrying a die pad it? which is vertically reciprocable in the die shoe 16. The bolster 18 is provided with one or more cylinders 22, each having a piston 24 reciprocable therein and engaging the underside of the die pad 2% The bolster is provided with a passage 26 which is connected by a conduit 28 to a valve assembly including body 3%.

The valve body 30 is provided with a passage 32 connected to the conduit 28 and terminating in a cavity or recess 34 containing a check valve 36 which engages a valve seat 38 and is urged against the valve seat 38 by a spring 4!). A passage 42 leads from the valve seat 38 to a passage 44 communicating with a conduit 46 connected to a supply tank 43 which contains a quantity of hydraulic fluid under pressure (for example, lbs. p.s.i.).

The valve includes a passage 5t? which intersects the passage 32 and communicates with a valve chamber 52 containing a pressure relief valve 54 which is adapted to close the passage 5i under the influence of a spring 56 which is backed up by an adjusting screw 53 threaded into a plug 60 which closes the upper end of the valve chamber 52. A passage 62 communicates with the valve chamber 52 on the downstream side of the pressure relief valve 54 and communicates with a conduit 64-, which is also connected to the supply tank.

A passage 66 forming an extension of the passage 42 communicates with a passage 68 which intersects the passage 62 past a check valve 7%, which is engaged by a spring '72 reacting against an adjusting screw 74. In the idle position of the press, check valve 78 has tank pressure applied on both sides, plus a spring tension (applied by spring '72) considerably less than tank pressure.

Each cylinder 22 is filled with hydraulic fluid under pressure from the tank 48 during the return stroke of the press through conduit 46, passages 44 and 42, past check valve 36, and through passage 32, conduit 28, and passage 26. When the ram 12 descends during the working stroke of the press, the die pad 2% is forced downwardly against the piston 2a (or pistons, as the case may be) which resists such movement of the die pad to an extent determined by the pressure at which the pressure relief valve 54 is set to open. When the die pad retracts, the pressure fluid is forced out of the cylinder 22 through conduit 23 into passage 5%, and when the pressure exceeds a predetermined amount, the pressure relief valve 54 will open to allow the fluid to return to the supply tank 48 through passage 62 and conduit 64 at a portion of the cycle when the velocity of the displaced hydraulic fluid is very high.

The rate at which the pressure fluid is expelled from the cylinder 22 (or cylinders, as the case may be) is proportionate to the rate of closing movement of the ram 12. Since the ram is driven by a crank, its downward movement will be at a greater speed when the crank arm is horizontal and will be gradually slowed as the ram reaches the lower limit of its travel. The passages 66 and 68 and the check valve 70 constitute a means for providing additional passage area (through passage 46) for the flow of fluid back to the tank during the working stroke of the press when the pressure on the fluid is the greatest. The increase in the passage area past the valve 54 reduces the velocity of the fluid flow, thereby reducing friction and the heat generated thereby. As the ram reaches the lower end of its travel, its speed is decreased to the point where the pressure on the fluid is reduced sufficiently so that valve 70 will close and the remaining pressure fluid will be forced out through the conduit 64 into the tank.

When the ram begins its return stroke, the valve 711 will be closed and the pressure within the tank 48 will force the hydraulic fluid through conduit 46 and passages 44 and 42 past check valve 36 to the cylinder 22. The ram travels upwardly at an increasing rate of speed as the crank arm moves toward its horizontal position and the piston 24 is therefore free to travel upwardly at a greater speed. It is desirable in some cases that the pad 20 follow the ram as it returns so as to strip the work from the lower die and to minimize the possibility of the pad cocking. Hence when and if the pressure in the lines 66, 32 and 28 drops as the ram moves up, tank pressure exerted on check valve '70 through lines 64 and 68 unseats valve 70 allowing oil to flow from lines 64 and 68 past valve 70 into lines 66 and 32, thus maintaining the pressure on piston 22 to cause the pad 20 to follow the ram to the extended or upper position of the pad 20. The valve 70 closes when the cylinders 22 are filled, and a new cycle of operation begins.

The invention is schematically illustrated in FIG. 2 in a hydraulic control circuit including a time delay valve for delayingreturn movement of the die pad after the ram has completed its working stroke. In this embodiment of the invention the ram 11% engages the work 102 which rests upon the die pad 104 engaged by pistons 106 working within cylinders 198. Any suitable number of pistons 106 and cylinders 168 may be used. The conduit 110 communicates with each of the cylinders 103 through an air bleed tube 112 or 114, which may be similar to those disclosed in my Patent No. 2,924,446, issued February 9, 1960. The piston and cylinder arrangement need not he of this particular type and may be of any suitable construction.

A valve body 116 is provided with a port 113 communicating with the conduit 110 and a second port 12% which communicates with the conduit 116 through a branch line 122. A passage 124 communicates with the port 118 and intersects a passage 126 which is provided with a check valve 128 which normally closes the passage 126 under the influence of a spring 136. A supply tank 132 containing hydraulic fluid under pressure is provided with a conduit 134 which leads to a passage 136 in the valve 116 communicating with the passage 126 through a bore 138. The cylinders 168 are fitlcd with hydraulic fluid under pressure from the supply tank 132 through conduit 134, passages 136 and 126, past check valve 128, passage 124, and port 118 to conduit 116.

The passage 120 is closed by a pressure relief valve 140 which is engaged by a spring 142 confined between the valve 141} and an adjusting screw 144. When the die pad 104 is retracted, the pistons 106 are forced downwardly to dispace the hydraulic fluid through the conduits 110 and 122 into passage 121i, and when the pressure of the hydraulic fluid exceeds a predetermined amount the pressure relief valve 140 will open, allowing the fluid to return to the tank 132 through passages 146 and 148 and conduit 150. The passage 146 provides a communication between the passage 12% and the passage 126 and is normally closed by a check valve 152 located at one end of the bore 138. When the pressure in the passages 146, 148 exceeds a predetermined amount during the working stroke of the press, the valve 152 will open to provide an additional passage for the return of fluid to the tank, consisting of the passage 136 and conduit 134, thus reducing the pressure and flow velocity in the return lines to the tank. On the return stroke of the ram, the valve 152 will open when the pressure dilferential between the pressure at which the fluid is maintained within the supply tank and the pressure in passage 126 exceeds a predetermined amount, thereby providing an additional passage area for the return of pressure fluid to the cylinders 108 during a portion of the cycle when the fluid velocity is highest.

The valve 116 shown in FIG. 2 is the same as the valve 30 shown in FIG. 1, except that it has a time delay valve incorporated therein to delay return movement of the die pad to its extended position upon opening of the press. The time delay valve comprises a spool valve 152 which is slidable within a bore 154 and urged toward the right-hand end of the bore by a spring 156 which is confined between the valve 152 and an adjusting screw 158. A portion of the pressure fluid ejected from the cylinders 108 upon closing of the press and flowing through passage 121 will be supplied to the bore 154 through a passage 160 past a reduced diameter portion 162 of the valve 152 to passages 164 and 168 to a passage 170 which leads to the right-hand end of the valve bore 154 to shift the spool valve 152 to the left until it closes the passage 126.

After the ram has completed its working stroke, the return of fluid to the cylinders 108 will be delayed due to the fact that the passage 126 is closed by the valve 152 and will remain closed until the fluid in the right-hand end of the valve bore 154 is forced out through passage 170 past a bleeder valve 172 into passage 126 ahead of the check valve 128. As soon as the time delay opens the passage 126, the pressure fluid will be returned to the cylinders 168 through the conduits 134 and 150 in the manner described. The time delay valve disclosed herein forms the subject matter of my Patent No. 2,901,- 23 8, issued August 25, 1959.

It will be apparent that the valve arrangement disclosed herein is very simple in construction and requires only three separate valves and a minimum number of passages in order to obtain the desired results. By employing two conduits connecting the supply tank to the valve body and a single conduit connecting the valve body to the working cylinder, the conduits lengths are greatly reduced and smaller lines can be used, which enables more of the hydraulic fluid tot be circulated back to the supply tank at each cycle of the press.

While I have illustrated and described preferred embodiments of my invention, it is understood that these are capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first passage connecting said cylinder and tank through which fluid under pressure is supplied from said tank to said cylinder and the piston therein to move said die pad to its extended position during the return stroke of the press, a check valve in said first passage preventing fluid flow therethrough from said cylinder to said tank, a second passage connecting said cylinder and tank through which fluid is returned from said cylinder to said tank during the working stroke of the press, a pressure relief valve in said second passage providing resistance to the return of fluid from said cylinder to said tank, a third passage connected into said first passage between said check valve and said tank and connected into said second passage between said pressure relief valve and said tank, and a normally closed valve in said third passage adapted to open to permit fluidflow from said second passage to said first passage and back to said tank thereby providing additional passage area for the return of fluid to said tank when the pressure in said cylinder exceeds a predetermined pressure during the working stroke of the press, said normally closed valve being adapted to open to permit fluid flow from said tank through said second passage into said first passage and to said cylinder thereby providing additional passage area for the flow of fluid to said cylinder when the pressure differential between said tank and cylinder exceeds a predetermined amount during the return stroke of the press.

2. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first passage connecting said cylinder and tank through which fluid under pressure is supplied from said tank to said cylinder and the piston therein to move said die pad to its extended position during the return stroke of the press, a check valve in said first passage preventing fluid flow therethrough from said cylinder to said tank, a second passage connecting said cylinder and tank through which fluid is returned from said cylinder to said tank during the working stroke of the press, a normally closed pressure relief valve in said second passage providing the sole resistance in said second passage to the return of fluid from said cylinder to said tank, a third passage connected into said first passage between said check valve and said tank and connected into said second passage between said pressure relief valve and said tank, and a normally closed check valve in said third passage adapted to open to permit fluid flow in parallel through portions of both said first and second passages back to said tank when the pressure in said second passage exceeds a predetermined pressure during the working stroke of the press and to permit fluid flow from said tank in parallel through said portions of both said first and second passages to said cylinder when the pressure differential between said tank and cylinder exceeds a predetermined amount during the return stroke of the press, each of said portions of said first and second passages communicating directly with said tank and being unobstructed whereby hydraulic fluid is free to flow in either direction in said portions relative to said tank.

3. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first passage connecting said cylinder and tank, a check valve in said first passage past which fluid under pressure is supplied from said tank to said cylinder and the piston therein to move said die pad to its extended position during the return stroke of the press, a second passage connecting said cylinder and tank, a pressure relief valve in said second passage past which fluid is returned from said cylinder to said tank during the working stroke of the press, a third passage connected into said first passage between said check valve and said tank and connected into said second passage between said pressure relief valve and said tank, a normally closed valve in said third passage adapted to open to provide additional passage area for the return of fluid to said tank when the pressure in said second passage exceeds a predetermined pressure during the working stroke of the press and for the flow of fluid from said tank into said first passage when the pressure diflferential between said tank and cylinder exceeds a predetermined amount during the return stroke of the press, and a time delay valve in said first passage operable responsive to the flow of fluid through said second passage for closing said first passage to delay the refilling of said cylinder through said first passage on the return stroke of the press.

4. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first passage connecting said cylinder and tank, a check valve in said first passage past which fluid under pressure is supplied from said tank to said cylinder and the piston therein to move said die pad to its extended position during the return stroke of the press, a second passage connecting said cylinder and tank, a pressure relief valve in said second passage past which fluid is returned from said cylinder to said tank during the working stroke of the press, a third passage connected into said first passage between said check valve and said tank and connected into said second passage between said pressure relief valve and said tank, a normally closed valve in said third passage adapted to open to provide additional passage area for the return of fluid to said tank when the pressure in said second passage exceeds a predetermined pressure during the working stroke of the press, and a time delay valve in said first passage operable for closing said first passage to delay the refilling of said cylinder through said first passage on the return stroke of the press.

5. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first passage connecting said cylinder and tank, a check valve in said first passage past which rfluid under pressure is supplied from said tank to said cylinder and the piston therein to move said die pad to its extended position during the return stroke of the press, a second passage connecting said cylinder and tank, a pressure relief valve in said second passage past which fluid is returned from said cylinder to said tank during the working stroke of the press, a third passage connected into said first passage between said check valve and said tank and connected into said second passage between said pressure relief valve and said tank, a normally closed valve in said third passage adapted to open to provide additional passage area for the flow of fluid from said tank into said first passage when the pressure differential between said tank and cylinder exceeds a predetermined amount during the return stroke of the press, and a time delay valve operable for closing said first passage to delay the refilling of said cylinder through said first passage on the return stroke of the press.

6. In a ram type press having a movable die pad and a hydraulic cushion for said die pad comprising a cylinder and a piston reciprocable in said cylinder and reacting against said die pad, said piston being adapted to resist movement of said die pad to its retracted position during the working stroke of the press and to return said die pad to its extended position on the return stroke of the press, and a supply tank adapted to contain hydraulic fluid under pressure; means for controlling the flow of hydraulic fluid to and from said cylinder comprising a first conduit interconnecting said tank and cylinder and having only a single check valve therein past which hydraulic fluid is supplied from said tank to said cylinder under tank pressure, a second conduit interconnecting said tank and cylinder and having a normally closed pressure relief valve therein forming the sole resistance in such second passage to the return of fluid from said cylinder to said tank during the working stroke of the press, valve controlled bypass means interconnecting said conduits on the tank side of the said valves thereinwhereby to by-pass fluid from one conduit to the other conduit when the pressure of the 8 fluid in said one conduit exceeds a given pressure, said valve controlled by-pass means being disposed relative to said first and second conduits so as to be effective for bypassing fiuid on both the fluid supply and return cycles 5 of said system.

References Cited in the file of this patent UNITED STATES PATENTS Williamson July '8, 195 8 2, 890,669

Williamson June 16, 1959 

